Expansion circuit for oscilloscopes



8, 3945- H. A. THoMPsoN EXPANSION CIRCUIT FOR OSCILLOSCOPES Filed Aug. 3, 1940 3 Sheets-Sheet l 3, l945- H. A. THOMPSON EXPANSION CIRCUIT FOR OSCILLOCOPES Filed Aug.v s, 1940 3 sheets-snaai 2 Fig. a.

Figi.

` Inventor` Harris A.Thompson, by .1v/@7d JMM, HIS Attorney.

May 8, i945. H. A. THOMPSON 2,375,709

EXPANSION CIRCUIT FOP. OSCILLOSCOPES Filed'Aug. 3, 1940 5 Sheets-Sheet 3 Patented May 8, 1945 UNITED STATES PATENT OFFICE y 2,315,109 I y A EXPANSION cmcm'r Fon osomnoscorns Harris A. Thompson, Detroit, Mich., nss'lgnor to General Electric Company. a corporation of New York Application August 3, 1940, Serial No. 350,409

1s claims. (ci. 315-22) i My invention relates to Oscilloscopes and concerns particularly Oscilloscopes of the type having a signal-tracing beam, such as cathode ray osciltriangular voltagev wave. The arrangement is f such that the return or ily-back portion of the loscopes, with means for detlecting the beam in My invention is a modification of that disclosed in the copending application of Ellsworth D. Cook, led June l, 1940, Serial No. 338,360, issue January 30, 1945, as Patent 2,368,448, assigned t the same assignee as the present application rep lating to an oscilloscope and a sweep wave generator therefor having such a shape of sweep wave that a portion of the signal wave may be considerably expanded, that is, maybe made to cover a considerably greater distance along the time axis on the oscilloscope screen than the remainder of the wave.

It is an object of my invention to provide .a simplified arrangement for obtaining the expansion of the wave.

It is also an object of my invention to provide an arrangement for increasing thebrilliancy of the expanded portion of the wave appearing on the oscilloscope screen.

It is still another object of my invention to provide an improved arrangement for varying the phase relationship of the elements of the sweep wave in order to select the portion of the signal wave to be expanded independently of frequency or Wave shape of the signal wave.

Other and further objects and advantages will become apparent as the description proceeds.

In carrying out my invention in its preferred form in connection with cathode ray Oscilloscopes having deflection plates for electrostatic deflection of the beam, I provide a discharge tube circuit for producing a triangular sweep wave of voltage for application to the horizontal or sweep plates of the cathode ray oscilloscope and producing also a rectangular voltage wave for injection in the circuit energizing the vertical or signal-responsive deflection plates of the oscilloscope, in order to oiT-set the expanded portion of the signal wave. I provide a rectangular voltage wave also for application to the control grid of the cathode ray oscilloscope for increasing the fly-back brightness of the beam.

For selecting the portion of the signal wave to be expanded I provide a. phase shifting circuit interposed between the signal wave, or a voltage synchronized therewith, and the input electrode triangular voltage wavel is much shorter in its duration than the time for the forward sweep so that the portion of the signal wave occurring during the fly-back interval is greatly expanded and appears in reversed position on the oscilloscope screen. The ofi-setting voltage" serves to separate the expanded portion from the remainder Qi' the wave on the oscillascope screen to avoldconfusion. It will be understood that in the case of Oscilloscopes with eelctromagnetic deection coils, a current of triangular wave kshape instead of a voltage is produced in' th sweep circuit.

My invention will be understood more readily from the following detailed description when considered in connection with the accompanying drawings and those features of the invention which are believed to be novel and patentable will be pointed out in the claims appended hereto. In the drawings Fig. 1 is a diagram of one embodiment of my invention representing the principal eelctrlcal circuits and schematically representing various elements of a cathode ray oscilloscope. Fig. 2 is a series of graphs illustrating the principle of my invention. Fig. 3 is a representation of a ligure which may be produced by my apparatus on an oscilloscope screen when examining a sine wave, and Fig. 4 is a circuit and schematic diagram of a modification in the arrangement of Fig. l. Fig. 5 is a graph illustrating the eiiect of an adjustment in the circuit of Fig. 4. Like reference characters are utilized throughout the drawings to designate like parts.

Referring to Fig. 3 there will be seen a sine wave!! I with the end portion I2 thereof dotted.

Corresponding to the dotted portion I2 there isl an expansion thereof I3 of the same length as the remainder of the sinewave II, but off-set therefrom and reversed in direction of horizontal progression. In the case of irregular wave shapes it may be highly desirable to expand some particular portion of the wave, such as the portion I2, for'more precise examination. Such expansion and reversal of the portion I2 of the wave to produce the segment I3 is accomplished in my apparatus by producing a sweep voltage wave I II of the shape shown in curve D of Fig. 2. In order that thesegment I3 of the wave will not be diminished in brightness by its increased speed across the oscilloscope screen, abrightness-increasing voltage is applied to the control electrode of the oscilloscope tube in a manner which of the discharge-tube circuit for producing the will be described hereinafter. To permit expanding any selected portion of the wave II to be examined, the phase relationship between the sweep wave I4 and the signal wave is varied in a manner which will also be described hereinafter.

The signal wave or the sine wave fundamental thereof, if the signal wave is not a sine wave, may be represented by the sine wave I5 constituting the curve A of Fig. 2. The sweep wave is produced by rst producing an irregular wave I6 with steep-sided loops, as shown in curve B of Fig. 2, which wave may be adjusted in frequency in order to correspond in frequency to the signal wave so that it may be synchronized therewith. The irregular wave I6 is then converted into a rectangular wave I1, constituting the curve C ol Fig. 2, and the rectangular wave l1 is converted into a triangular wave I4, curve D. In order to off-set the expanded portion of the wave I2 from Fig. 3, a rectangular wave synchronous with the triangular wave is injected in the vertical ampliiler for producing the signal wave so that the voltage applied to the signal deiiection plates is as represented in curve I3 in graph E of Fig. 2. The rectangular wave injected in the vertical amplifier is of the opposite polarity from the rectangular wave I1, if the expanded portion of the wave is to be off-set in the positive direction and trode -provided in the vertical ampliiler 32. The vertical ampliiler 32 may be of the conventional type consisting oi' one or more stages or vacuum tube circuits except that it includes suitable means for adding together two input voltages. Such adding means may take the form of a mixer tube 35, forming one stage, preferably the initial stage of the vacuum tube amplifier circuit. The power supply and output connections for the tube 35 are not shown since it will be understood that these are the same as in conventional vacuumtube amplifiers. The mixer tube 35 has two control electrodes 36 and 31 to which the input signal derived from the terminals 23 and the rectangular wave from the connection 33 are applied respectively.

The mixer tube 35 may bea tetrode in which the control electrode 38 constitutes the usual control grid, and the control electrode 31 constitutes the usual screen grid. In this case, it is desirable to apply a voltage of sumcient amplitude tothe may be of the same polarity if the expanded portion is to be offset in the negative direction. By

varying the phase relationship between the sweep wave I4 and the signal wave I5, any desired portion of the signal wave may be off-set and expanded, as illustrated in the dotted curve I9 of graph E, Fig. 2, in which for convenience the phase angle of the signal wave is shown as varied while the phase angle of the sweep wave is the same as for the other graphs of Fig. 2.

Referring to Fig. 1 there is illustrated a cathode ray oscilloscope tube 2| having a screen 22 in which the wave shape of an input signal applied at terminals 23 is to be examined. Responsive to the input signal 23 there is apparatus shown Within the dotted rectangle 24 for varying the phase relationship of the fundamental component of a voltage reproducing the input signal. The output voltage of the phase shifting circuit 24 is supplied to a synchronizing amplifler. 25, the output of which in turn controls and synchronizes a r multi-vibrator circuit 26 for producing the irregular wave I6. The irregular wave I6 is fed to a clipper circuit 21 to produce a rectangular'output wave I1 and the output of the clipper circuit is applied to a saw tooth generator circuit to provide a triangular wave I4. The output of the saw tooth generator 23 is connected to the sweep wave circuit of the oscilloscope 2l. The oscilloscope 2l is illustrated as being of the electrostatic beam-deilection type and thus the sweep-deilection circuit includes a pair of horizontal-deflection plates 29. The extension to the magnetically deected oscilloscope is obvious to one skilled in the art. Preferably a horizontal amplifier 30, which may be of conventional type, is interposed in the horizontal-deiiection circuit.

The input signal is applied to the vertical deiiection circuit including signalor vertical-deflection plates 3|, prferably also through an amplifier 32 represented schematically by the rectangle bearing the legend, Vertical Amplifier. For off-setting the portion of the wave which is to be expanded, a connection 33, preferably through an injector amplifier 34, is made between a suitable portion of the rectangular-wave generator or clipper circuit 21 and a suitable elecscreen 31, 'and it is therefore advantageous to have the injector amplifier 34 interposed in the connection 33 if the olf-setting wave is applied to the screen 31. If such an injector amplifier is not employed, it may be preferable to apply the input signal to the screen 31 and the off-setting i wave to the grid 36 or in some other well known manner. In the arrangement illustrated, it may be desirable to provide a volume control 33 to permit adjusting the strength of the input signal applied to the vertical amplier 32. A decoupling or by-pass condenser 31' may be connected between ground and the screen 31 through a relatively loW-resistance resistor 35 in order not to short circuit the oil-setting wave.

The cathode ray oscilloscope tube 2l is of the well known type including in addition to the defiection plates 29 and 3l, a cathode 39, an anode not shown, and a control electrode 40 for controlling the intensity of-the beam. In order to increase the strength of the beam during the quick return or ily-back period 4I of the saw tooth sweep wave I4 for maintaining the apparent brilliancy of the extended segment I3 of the signal `curve on the oscilloscope screen in spite of the -increased during the y-back period. 'I'hls may be accomplished by means of a connection 42 to a point in the rectangular wave generator or clipper circuit 21 on which a short positive pulse appears during the fly-back period, as will be explained more in detail hereinafter. For the purpose oi.' maintaining the control electrode 40 sufficiently high in potential with respect to the cathode 39, the conventional power supply for the tube 2 I, not shown, may be so arranged as to supply a voltage to the cathode 39 which is suiliciently 'negative with respect to the ground connections shown for the square Wave generator 21.

The phase shifting circuit -indicated in the dotted rectangle 24 may be of any suitable type.

' The specific arrangement illustrated in Fig. l for phase-shifting a voltage that can be synchronized with the signal wave, not being my invention per se, need not be described at length. It consists of a conventionalcondenser-rheostat type of phase shifter including a condenser 43 connected in series with a rheostat 44 across the secondary winding 45 of a transformer. The common terminal 46 of the condenser 43 and the rheostat 44 serves as the output terminal of the phase shifter circuit 24 for connection to the synchronizing amplier 25, and the mid point of the transformer.

winding 45 is connected to the same ground connection as the synchronizing ampliiier 25. A po larity-reversing switch 41 may be provided to extend the range of the phase shifter from 180 to 360 degrees and if the wave shape of the input signal is liable to be too distorted to permit effective operation of a simple form of condenserrheostat, phase-shifter 43-44, suitable means for extracting the sine-wave fundamental such as a filter 48 may be interposed between the polarity reversing switch l1 and the input terminals 23 to which the-input signal, or a fraction thereof is connected.

The synchronizing amplifier 25 may be any suitable amplifier of conventional design. The form shown is a conventional triode amplifier including a three-element discharge device 49 having its control electrode 50 coupled to the output terminal 45 of the phase shifting circuit 24 through a coupling condenser The multi-vibrator circuit 26 comprises a pair of triodes 52 and 52', each having its anode coupled to the control electrode of the other through one or the other of the coupling condensers 53 and 54. A control electrode 55 of one of thetubes 52 is coupled by means of a coupling condenser 56 to the anode or output terminal 51 of the synchronizing amplifier 49 The anode connection 58`of the other triode 52h serves as the output terminal of the multi-vibrator 26. For permitting adjustment of the frequency of the wave I5 produced by the multi-vibrator 26. a potentiometer 59 is provided having an adjustable tap 60 to which the control electrodes of the tubes 5I and 52 are connected through grid leak resistors 6| and 52, respectively. The relative values of the resistances in the resistors 6l and 52 are chosen to give the desired ratio between the positive and negative pulse widths of the wave I 5.

The clipper circuit 21 comprises a pair of vacuurn tubes '63 and 65 with the control electrode 65 of the rst vacuum tube 53 coupled through a coupling condenser 66 to the anode terminal 58 of the tube 52` the terminal 58 being the output of the multi-vibrator 25. The control electrode 51 of the clipper tube 66 is coupled through the coupling condenser 68 to the anode 69 of the iirst clipper tube 63, and the anode connection of the second tube 60 serves as the output terminal of the clipper circuit 21. In order to provide a rectangular -wave of opposite polarity from the wave appearing at the terminal 10, a resistor 1l may be connected in the cathode lead of the tube 6d with the injector or loli-setting voltage connection 33 being taken from the cathode 12 of the second clipper tube 64. 'I'he ily-back brightness` control through the connection $2 may be taken from the anode 69 of the first tube 63.

The saw tooth generator circuit 28 consists of a resistor 13 connected in series with a condenser across the anode-cathode circuit of the second clipper tube Sli, the resistor 13 being connected to the clipper tube anode 15, and the condenser 15 being connected to ground, with the common terminal 15 serving as the saw-tooth wave output terminal connected through a conductor 16 to the input terminal of the horizontal amplifier 30. The vacuum tube circuit -21. inclusive. is shown with resistance coupling, and accordingly suitable anode resistors 11 of proper individual values are connected in the anode leads.4

Suitable sources of plate voltage and heater current are provided forv the discharge tubes specifically shown and for the ampliiiers 30, 32 and 36. However, since these-arrangements are well known in the art they need not be illustrated. The connection to the positive terminal of the source of plate voltage is represented by the terminal 18. Although triodes have been illustrated for the sake of simplicity'in the drawings, it will be understood that my invention does not exclude the use of multi-electrode tubes, Where they may be advantageous in accordance with the practice of those skilled in the art. Various conventional features of the circuits such as gridleak resistors, stabilizing negative feed-back resistors in the cathode leads, by-pass condensers, and ripple-absorbing condensers across the anode circuits, -have been illustrated without specific mention, as these are not distinctive features of my invention and their use is according to wellknown principles.

The principle of operation of the circuits is represented by the series of characteristic curves reproduced along the lower margin of Fig. l with the arrows pointing to the points in the circuit at which the characteristic curves are produced. Thev curve I5 represents an input signal or a fundamental 'sine w'ave component thereof, and the curve l5' represents the corresponding curve shifted in phase by means of the phase shifting circuit 26.

The voltage I5' is amplied by the synchronizing amplifier 25 and isapplied to the control electrode 55 of the multi-vibrator tube 52. 'I'his multi-vibrator is adjusted to have almost the same fundamental frequency as that of the Wave applied from the synchronizing amplifierv 25. When the sum of the potentials on the control electrode 55 passesA through a critical potential, conduction current is allowed to flow in the anode circuit of tube 52 of multi-vibrator 26 lowering the anode potential and thereby driving the control electrode of tube 52past cut-oil' of anode current abruptly and causing the anode potential of tube 52' to rise abruptly as represented by one of the vertical lines, such as the vertical line 80 in the multi-vibrator output, curve i5. The current shift takes place abruptly since each control grid of the multi-vibrator is tied through the cono densers 53 and 54 to the anode of the other tube. The grid condensers 53.and 54 thereupon have charges representing a state of unstable equilibrium and tend to discharge along curves of well-known form until the control electrode of the then non-conducting tube 52 passes through that grid potential corresponding to cut-ofi of plate current, the said change of Vgrid potential lbeing in positive direction whence the action is shifted to that tube and the process continues, shifting abruptly from one tube to the other continuously as villustrated by curve I6. The vertical line 19 represents the abrupt drop in anode potential of the tube 52 when that tube takes current. The portions 8| and 82 of the curve l5 represent the eiect of the discharge curves of the condensers. In the absence of synchronizing voltage i5. the shifting of current from one tube to the other takes place repeatedly at a frequency `determined by the setting of the tap 50.' higher frequency being produced by raising the average potential of the tap and lower frequency being produced by lowering the potential of the-tap 60. However, if the frequency is set relatively close to the frequency of the input signal tied to the multi-vibrator 26 through the coupling condenser 56, the oscillations of the multi-'vibrator will be synchronized with the input signal so that the 'current shifts take place at a predetermined point-in the input signal wave.

The relationship between the resistances of the eiresistors @i and @iii is made such that the negative pulse width. that is, the horizontal distance along made relatively small in the comparlsonwvith the positive pulse Width, the width of the portion 82 in order that the fly-back portion 4i of the sweep wave will be steep, representing rapid beam movement to give a large expansion of the portion or the signal wave to be examined in detail.

The characteristics of the clipper tubes 21 are such that the minimum voltage alongl parts 8i and B2 `in either loop of the wave I6 exceeds the cut-off voltage of the clipper tube so that these parts are cut-off and the resultant amplified voltage appearing at the terminal 10 is rectangular.

es shown by the curve il. It will be understoodthat one clipper tube cuts ofi one half of the loop it and the second tube cuts off the other half.

The resistor 13 of the saw tooth generator 2&3 has a resistance which is relatively large inyrelation to the capacitance of the condenser 14 so that the current flowing through the resistor 13 is substantially proportional to the potential of the terminal "it, regardless of the frequency or steepness of the wave iront of the potential. The condenser it, however, has an integrating effect and the rectangular wave i1 is converted into a saw tooth or triangular wave it. Looked at another way, since the rectangular wave l1 produces constant voltage ofone polarity at the terminal 1@ alternating with constant voltage of the opposite polarity and resistance 13 predominates by a large margin in circuit 12S-14, the current in the resistor 'i3 remains constant as long as it continues with one polarity, causing the condenser charge and potential difference across it to vary at a uniform rate, but owing to the diierence in heights of the positive and negative loops from the average value of the rectangular wave i1, the magnitude of the charging current is considerably greater during the short negative pulse than during the longer positive pulse. Consethe time axis of the portion an or the curve It, 1s

quently, the voltage in the wave it builds up grad- 1 ually at a uniform rate, and falls off again uniformly at a quicker rate to produce a substantially perfect triangular or saw-tooth wave which is applied to the horizontal plates 29 through tlie horizontal amplifier 3U. In the portion 83 of the triangular wave it, the cathode ray beam is swept forward at a uniform rate to produce the prin-` cipal portion of the signal wave on the cathode ray screen 22 and during the quick return portion ti of the triangular wave it, the cathode ray beam is swept back more rapidly, but also at a uniform rate to produce the expanded segment i3 of the signal wave (Fig. 3). The wave i4, being triangular, has two portions of diierent slope, the portion 83 being shown with positive slope and the portion ti with negative slope.

I have described and illustrated the use of the multi-vibrator circuit with clippers and the sawtooth circuit for producing a triangular sweep wave, because such a circuit is particularly well adapted for working in the high frequency limit of the sweep circuits. My invention, however, is not limited to the specic arrangement illustrated and obviously does not exclude the use of a gas discharge tube to create the necessary triangular or saw-tooth wave.

Since in vacuum tube circuits, the plate polarity reverses from one stage to the next, a short negative voltage pulse on the anode connection 1U of the clipper tube 64 occurs simultaneously with a short positive pulse on the anode 69 ofthe preceding clipper tube 63. By reason of the connection 42 from the clipper-tube anode 69 to the control electrode 46 of the cathode ray tube 2l, the beam intensity of the cathode ray tube is increased during the short pulse when the beam is being swept back rapidly to produce the expanded portion of the signal wave. Likewise, since the anode voltage oi' the discharge tube is at c. minimum when the anode current is at a maximum, the voltage across the resistor 1| in the cathode circuit of the clipper tube 64 is at a maximum during the short pulses, and a rectangular wave 34 with short-pulse positive-voltage is injected in the vertical ampliiier 32 during the period when the beam is being swept back rapidly for expansion. Assuming that the amplier has such a number of stages as to reproduce the input polarity, the expanded portion/ of the wave is o-set in the upwards or positive direction. By a change of connections the expanded portion of the wave could also be off-set in the opposite direction.

In the arrangement illustrated in Fig. 4 the general features of the circuit shown in Fig. 1 are employed with certain reilnements. The phase shifter circuit 2t of Fig. 1 is replaced by a modified form of phase shifter circuit 84 shown in the lower half of sheet 2, which is capable of producing a time delay of substantially .any desired portion of the period of the signal between the signal wave and the sweep wave, regardless of the wave shape or frequency of the signal wave, or the availability of a substantially sine wave which can be synchronized with the signal wave. The phase shifting circuit 84 illustrated in Fig. 4 comprises a discharge tube circuit which may employ conventional vacuum tubes including one or more buffer stages or synchronizing amplifier stages t5, a multi-vibrator circuit 88, and a clipper circuit @'Lwith resistance-capacitator coupling between stages. The buffer 85, as illustrated, comprises two stages similar to the synchronizing amplier 25 illustrated in Fig. 1 with the control electrode Se of the first stage connected through a volume control t@ and a coupling condenser 90 to a source of synchronizing voltage which may be the signal wave itself or a voltage proportional thereto. In the arrangement illustrated, a modied form of vertical amplifier 32' is indicated with a connection 9i providing the synchronizing voltage. It will be understood that the connection ti is merely brought out in the conventional manner from some suitable point in one of the stages of the vertical amplifier 32 at which a voltage appears, corresponding to the input signal voltage wave.

The multi-vibrator 86 is similar in principle of operation to the multi-vibrator 26 previously described, with the synchronizing connection from the synchronizing amplier being made in this case, however, by means of a coupling condenser 92 joining the output terminal 85 of the buffer 85 and the first anode 93 of the multi-Vibrator B8 which is capacitively coupled to the grid of the other half of the multi-vibrator. Twin triodes are illustrated in the phase shifting circuit 84 but it will be understood that these are the equivalent of separate tubes. The multi-vibrator 86 has an additional potentiometer 9B provided between the grid-leak resistors and 96 in order that the relative pulse widths of the multi-vibrator 86 may be adjusted. If the tap 91 of the potentiometer 94 is in one extreme direction the positive pulses are made very long in the direction of the time axis and the negative pulses are made very short, and vice Versa if the tap 91 is moved to the other extreme direction. An additional potentiometer 59 is connected across the B tube 2l, and with a control as the saw-tooth wage supplied to the sweep I supply so that the fundamental frequency of multi-vibrator 86 may be adjusted by moving a tap 69.

The clipper circuit 81 is also simllar 1n principle of operation to the clipper circuit 21 previously described, with a connection 98 being made to the second cathode at the upper end of a cathode resistor 99 so that a rectangular wave appears on the connection 98.- A saw-tooth generator circuit l consisting of a resistor IGI, and a condenser m2. connected in series across the output of the clipper tube 81 and having an output conductor 03, may be provided for furmshing a saw-tooth wave |03' for any purpose for which sucha wave may be dsired, corresponding in time division of the various parts of its cycle to the rectangular wave output of the clipper 81. The connection 98 is brought to the control electrode 50 of the synchronizing ampliler 25 through a. coupling condenser |04 and a. volume control 05, so that a synchronizing pulse amplied by the amplifier 25 occurs at the frequency determined by the frequency of the rectangular wave produced by the circuit 84, but the instant in each cycle of the output wave of the circuit 34 at which the sweep wave is initiated in the multi-vibrator 26 is determined by the relative time allotted by adjustment of 91 to the negative pulse out of the complete cycle as shown in Fig. 5. 'Ihe synchronizing of multi-vibrator 26 through its synchronizing amplier 25 is therefore determined by the instant within the cycle at which the polarity of the pulse changes from positive to negative in the rectangular output wave 98' v(Fig. 5) ofthe phase shifter circuit 84. This instant, in turn, is determined bythe length of the positive pulse. The pulse with adjustment by means of the tap 91 of the multi-vibrator 86, ac-

cordingly, serves as the phase shifting adjustment for the sweep wave generator shown in the upper half of Fig. 4. Since this depends merely on changing the relative length of the positive and negative loops of the rectangular wave provided by the phaseshifting circuit 84, it is independent of the wave shape of the input signal. In Fig. 5, the full lines represent the wave produced with one setting of the potentiometer 94, and the dotted lines represent the wave produced with another setting.

If desired, a pulse width adjusting potentiometer .I 96 may be provided in the multi-vibrator 26 in order to permit varying the length of the portion of the input signal which is expanded by varying the relative lengths of the positive and negative pulses provided by the multi-vibrator 25 which. in turn, determines Vthe relative duration of the ascending and descending portions of the saw-tooth wave id. L

If desired, also an additional vacuum tube stage may be provided for controlling the ily-back brightness, and the arrangement may be such that the ily-back brightness may be adjusted. For this purpose a beam-brightness control tube 401 may be provided which is shown as a pentode with an anode m8 connected through a coupling condenser 09 to the control electrode 40 and necessary resistors not shown, of theoscilloscope electrode H9 connected through a coupling condenser ill, to an adjustable tap H2 of the potentiometer H3,

which is connected between the anodes 69 and 10 Y of the clipper 21.' Since two clipper tubes 69 and 'III are available, the plate potentials vary in op posite directions and a rectangular wave lof adjustable amplitude but with the same pulse width v means for injecting a rectangular plates 29 may be obtained by adjustment of the tap H2. The rectangular wave appearing at the tap |12, in turn, controls the output of the brightness-control tube |91 in order to adjust the magnitude of the control electrode voltage of the oscilloscope tube 2l in accordance with the length and frequency of the ily-back portion vof the wave 4|.

I have herein shown and particularly described certain embodiments of my invention and certain methods of operation embraced therein for the purpose'of explaining its principle and showing its application but it will be obvious to those skilled in the art that'many modications and variations are possible and I aim, therefore to cover all such modications and variations as fall within the scope of my invention which is dened in the appended claims. 4

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A sweep wave generator for an oscilloscope producing a signal-trac' g beam and having sweep and signal deection circuits, said sweep wave generator comprising a synchronizing ampliner with means for controlling it by a voltage in synchronism with the signal wave to be examined in the oscilloscope, a multi-vibrator controlled by the synchronizing amplifier and including adjusting means for causing the multivibrator to produce a wave adjustable in frequency and pulse width, a clipper connected to theV multi-vibrator for converting the multivibrator wave into a rectangular wave, a saw? tooth circuit for converting the rectangular wave into a triangular wave, means for adjustably sluiting the phase of the triangular wave in relation to the signal wave, means for supplying a voltage synchronized with the rectangular Wave to the oscilloscope for. increasing the fly-back brightness of the oscilloscope beam, means for adjusting the magnitude of said voltage, and wave. in the signal deection circuit of the oscilloscope in synchronism with the triangular wave, whereby a portion of the signal wave is produced on the oscilloscope screen in expanded form reversed with respect to the remainder of olf-set therefrom.

2. A sweep-wave generator for an oscilloscope having sw'eep and signal deflection circuits and a beam-brightness determining electrode, said sweep wave generator comprising means for producing a rectangular wave, means for synchronizing said wave with the wave of the signal to be examined in the oscillosco and means 'for varying the phase relationship between the rectangular Wave and the signal Wave, means for converting the rectangular wave into a triangular wave, means for applying the triangular wave to the sweep deflection circuit Iof the oscilloscope, means for applying a voltage synchronized with said rectangular wave means for injecting a rectangular wave sychronized with said rst-mentioned rectangular4 wave in the signal deflection circuit of the oscilloscope, whereby a portion of the signal wave is produced on the oscilloscope screen in expanded form reversed with respect to the rethe wave and to the beam-brightness determining electrode of the oscilloscope. and

interval of the beam represents in reverse an oscilloscope beam, said sweep wave generator combination comprising means for producing a triangular sweep Wave having an amplitude representing the length of the time or sweep axis, having a forward portion and having a return portion whichv is shorter than the forward portion, means for synchronizing the triangular wave with a voltage which is in synchronism with the signal wave to be examined in the oscilloscope, means for applying the triangular waves to the sweep deilection circuit of the oscilloscope, and means for varying the phase relationship between the triangular wave and said last-mentioned voltage, means for supplying a voltage of increased value to the beam-brightness determining electrocle of the oscilloscope during the return portion of the triangular wave, whereby the beam brightness during the return is maintained comparable with the brightness during the advancing portion of the wave produced on the screen of the oscilloscope, and the return sweep of the beam represents in reverse an expansion of a portion of the signal wave.

4. In a sweep wave generator for a sectional wave expansion type oscilloscope including means for producing a triangular sweep wave, said means having a synchronizing electrode to which may be applied a voltage in synchronism with the signal wave to -be examined in the oscilloscope, a synchronizing terminal with means for energizing it synchronouslyl with the signal wave a phase shifter interposed between said synchronizing terminal and the synchronizing electrode of said triangular wave generating means, said phase shifter comprising a synchronizing amplifier connected to said synchronizing terminal, a multi-vibrator controlled by the output of the synchronizing amplifier and having adjusting means Ifor producing a peaked wave adjustable in frequency and adjustable in relative length of the positive and negative pulses, a clipper connected to the multi-vibrator for converting the multi-vibrator wave into a rectangular wave, and means for supplying the rectangular wave to the synchronizing electrode of the triangular-wave generating means to serve as a synchronizing pulse, whereby the adjustment of the pulse width varies the instant of initiation of the synchronizing pulse produced by the phase shifter without varying the frequency thereof in order that any portion of the signal wave may be expanded with respect to the remainder of the signal wave.

5. A sweep wave gener tor combination for an oscilloscope having a sweep deecting circuit for the oscilloscope beam, and an electrode for determining the brightness of the oscilloscope beam, said sweep wave generator combination comprising means for producing a, triangular sweep wave having a forward portion, and a return portion which is shorter than the forward portion, and means for supplying a voltage of increased value to the beam-brightness determining electrode of the oscilloscope during the return portion of the triangular wave, whereby the beam brightness during the return interval of the beam is maintained comparable with the brightness during the advancing portion of the wave produced on the screen of the oscilloscope, and the return sweep of the beam expansion of a portion of the signal wave.

6. A sweep wave generator combination for an cscillo'scope having a sweep deilecting circuit a generator of a for the oscilloscope beam, said sweep wave generator combination comprising means for producing a-t'riangular sweep wave having a forward portion of amplitude corresponding to the desired length of time axis and having a return portion of the same amplitude but which is shorter in time duration than the forward portion, means for synchronizing the triangular wave with a voltage which is in synchronism with the signal wave to be examined in the oscilloscope, and adjustable means for varying the phase relationship of the short return portion of the triangular wave with the signal to be examined, whereby the return sweep of the beam produces in reverse an expansion of a portion of the signal wave, and the portion to be expandedmay be selected by adjustment of the said phase varying means.

7. A sweep wave generator for an oscilloscope producing a signal-tracing beam and having sweep and signal deflection circuits, said sweep wave generator comprising a synchronizing amplii'ler with means for controlling it by a voltage in synchronism with the signal wave to be examined in the oscilloscope, a multi-vibrator controlled by the synchronizing amplier and having adjusting means for producing a wave adjustable in frequency and pulse width, a clipper connected to the multi-vibrator for convertingthe multi-vibrator wave into a rectangular wave, a saw-tooth circuit for converting the rectangular wave into a triangular wave, means for adjustably shifting the phase of the triangular wave in relation to the signal wave, and means for injecting a rectangular wave in the signal deflection circuit of the oscilloscope in synchronism with the triangular wave, whereby a portion of the signal wave is produced on the oscilloscope screen in expanded form reversed with respect to the remainder of the wave and off-set therefrom.

8. A sweep Wave generator combination for an oscilloscope producing a signal-tracing beam and having sweep and signal deilection circuits, said sweepv wave generator combination comprising triangular wave which thus has two portions of different slopes, the wave amplitude representing the time axis of the oscilloscope, one wave portion being steeper than the other, means for adjustably shifting the phase of the triangular wave in lrelation to the signal wave, a generator of a rectangular wave having a pulse length equalling the length of the steeper portion of the triangular wave and synchronized therewith, and means for injecting the r'ectangular wave in the signal deflection circuit, said oscilloscope being capable of producing a signal- .tracing beam of sulcient strength to produce a trace on the oscilloscope screen at the sweep speed produced by the steeper slope portion of the triangular wave, whereby a portion of the signal wave is produced on the oscilloscope screen in expanded form reversed with respect to the remainder of the wave and off-set therefrom.

9. A sweep wave generator combination for an oscilloscope producing a signal-tracing beam and having sweep and signal deflection, circuits, said sweep Wave generator combination comprising a generator of -a triangular wave with forward and return sweep portions, the wave having an amplitude representing the length of the time axis of the oscilloscope, one of said portions being steeper than the other, a generator of a rectangular wave having a pulse length correing .an amplitude representing the length of the.

spending to the length oi the steeper slope portion of the triangular wave and synchronized therewith, and means for injecting the rectangular wave in the signal deection circuit, whereby a portion of the signal wave is produced on the oscillscope screen in expanded form reversed with respect to the remainder of the wave and off-set therefrom.

10. A sweep wave generator combination `for an oscilloscope producing a signal-tracing beam and having sweep and signal deiiection circuits, said sweep wave generator combination comprising a generator of a triangular wave having forward and return sweep portions, one of which is steeper in slope than the other, the triangular wave having an amplitude representing the length of the time axis of the oscilloscope, means for adjustably shifting the phase of the triangular wave in relation to the signal Wave, whereby a portion of the signal wave is produced on the oscilloscope screen in expanded form reversed with respect to the remainder of the wave.

l1. A sweep wave generator combination for an oscilloscope having sweep and signal deflection circuits and a beam-brightness determining electrode, said sweep wave generator combination comprsing means for producing a rectangular wave, means for synchronizing saldi wave with the wave of the signal to Ibe Vexamined in the oscilloscope, means for converting the rectangular wave into a triangular wave, of amplitude representing the length of the time axis of the oscilloscope, means for applying the' triangular wave to the sweep deflection circuit of the oscilloscope, and means for applying a substantially xed voltage synchronized with said rectangular wave to the beam-brightnessdetermining electrode of the oscilloscope.

12. A sweep wave generator combination for an oscilloscope having a sweep detlecting circuit for the oscilloscope beam, and an electrode for determining the -brightnesso'f-the oscilloscope beam,

said sweep wave generator combination compristime axis oi the oscilloscope, meansfor synchronizing the triangular wave with a voltage which is in synchronism with the signal wave to be examined in the oscilloscope, means for varying the phase relationship of the triangular wave with the signal to be examined, and means for supplying a voltage to the beam-brightness determining electrode of the oscilloscope during the return portion oi the triangular wave, whereby the beam brightness during the return interval ci the beam' is brought to the desired value in relation to the brightness during the advancing portion of the sweep wave, and the beam produces in reverse an expansion of a portion of the signal wave.

14. In a sweep wave generator-for an oscilloscope having a sweep detlecting circuit for the oscilloscope beam and an elctrode for determining the brightness of the oscilloscope beam, said sweep wave generator comprising means forproducing a sweep wave with forward and retrace portions, the sweep wave having -an amplitude representing the length of the time axis of the oscilloscope, the combination with said brightness determining electrode of means for supplying a substantially fixed voltage thereto during one ofsaid portions of the sweep wave for maintaining a predetermined relationship between the beam brightness during the forward and retrace intervals of the sweep wave.

15. In a sweep wave generator for .an oscillo- I scope having a sweep deflecting circuit for the oscilloscope beam and an electrode` for determining the brightness of the oscilloscope beam, said sweep wave generator comprising means :for

producing a sweep wave including portions of different steepness, one of said portions having relatively great steepness and having an amplitude representing the length of the time axis of the oscilloscope, the 'combination with said brightness determining electrode of means for supplying a substantially ixed voltage thereto during said relatively steep portion of the sweep ing means for producing a triangular sweep wave with the portion of one slope steeper than the portion having the slope oi opposite polarity and being referred to as the return portion, means for synchronizing the triangular wave with a voltturn interval of the beam and the beam bright--A ness during the advancing portion oi' the sweep wave.

13. A sweep wave generator combination for an oscilloscope having a sweep deflecting circuit for the oscilloscope beam, and an electrode for determining the vbrightness of the oscilloscope beam, 1

said sweep wave generator combination comprising means ior^producing a triangular sweep wave having a return portion which is shorterv than the forward portion, the triangular wave havwave for maintaining a predetermined relationship between the beam brightness during said portion of the sweep wave and the brightness during another portion of the sweep wave.

16. In a sweep wave generator for an oscilloscope having a sweep deilecting circuit for the oscilloscope beam and an electrode for determining the brightness of the oscilloscope beam..

said sweep wave generator comprising means for producing a sweep wave including a portion of increased steepness for expanding a portion of the signal wave to be examined in the oscilloscope and of an amplitude representing the length of the time axis of the oscilloscope, the combination with said brightness determining electrode o! means for supplying a substantially lxed voltage thereto during the said steeper .portion of the sweep wave for maintaining a predetermined relationship between the beam hightness during the expansion interval of the sweep wave and the remainder of the sweep wave.

HARRISl A. THOMPSON. 

